The broad objective of this proposal is to test the hypothesis that increased intrarenal macrophage colony stimulating factor (CSF-1) expression is central to the pathogenesis of autoimmune renal disease in MRL-lpr/lpr mice. Using the MRL-lpr/lpr mouse with rapid, uniform, severe and predictable renal disease regulated by the lpr gene we will investigate the importance of CSF-1 in the pathogenesis of lupus nephritis. We propose to test whether the increase in circulating CSF-1 detected in neonatal MRL-lpr/lpr mice is contributed by the kidney alone or if other tissues are responsible for elevating serum levels. We will establish whether a molecule(s) in the circulation of MRL-lpr/lpr mice induces intrarenal CSF-1. We will determine whether increased renal expression of CSF-1 recruits macrophages. We will then investigate whether an increased expression of CSF-1 can induce renal disease in mice with normal kidneys including another strain with the lpr gene (C3H- lpr/lpr) and C3H-++ mice or accelerate an indolent, mild nephritis in congenic MRL-++, lacking the lpr gene. We will eliminate CSF-1 by creating a cytokine deficient MRL-lpr/lpr mouse and evaluate the impact on the development of lupus nephritis. In the event that the CSF-1 deficient MRL-lpr/lpr strain does not develop lupus nephritis we will determine if the inability of renal cells to express CSF-1 is responsible for preventing kidney disease. Through the advent of cellular and molecular techniques we now have the capacity to transfer a cytokine gene using a retroviral vector and establish tubular epithelial (TEC) and mesangial cell lines which can constitutively secrete high levels of a stable cytokine. By implanting these cells under the renal capsule we have created a system to introduce the continuing presence of CSF-1 (or other cytokines) into the kidney. We can then establish if CSF-1 recruits macrophages and determine whether CSF-1 will induce or accelerate renal injury in the MRL-++, C3H-lpr/lpr strains. To definitely establish whether CSF-1 or other cytokines have an enhanced glomerular expression prior to the influx of macrophages, we will isolate and pool individual glomeruli (glom) from MRL-lpr/lpr, congenic, and normal mice at varying ages and quantitate the level of cytokine and macrophages specific marker mRNA using the competitive template polymerase chain reaction. Finally, we will cross the MRL-++ or the C3H- lpr/lpr mice with CSF-1 transgenic mice and select for hybrids with these backgrounds overexpressing macrophage growth factors. In addition, we will eliminate CSF-1 from MRL-lpr/lpr mice by crossing them with the op/+ strain and select for a strain with op/op (producing a non-functional CSF-1) and lpr genes. By increasing or eliminating CSF-1, we will test the impact of this cytokine in promoting renal disease. In addition, we will use the approach of transplanting a kidney into a bilaterally nephrectomized recipient to determine when the MRL-lpr/lpr kidney is responsible for increasing serum CSF-1 and establish if this production is constitutive or is dependent on a stimulus. In addition, we will determine whether a circulating stimulant in the serum of MRL-lpr/lpr mice induces intrarenal CSF-1 and at what age this begins. Finally, we will test whether a kidney unable to express CSF-1 transplanted in the MRL-lpr/lpr mice develops renal injury. Taken together, using several novel approaches we will be able to clarify the importance of CSF-1 in the pathogenesis of lupus nephritis.